1. Field of the Invention
The present invention relates to a liquid crystal display apparatus of the supertwisted nematic type (hereinafter, referred to as "STN-LCD") provided with a phase difference plate as a color compensation plate, and particularly to a liquid crystal display apparatus such as a black-and-white STN-LCD which can be used in an OA (Office Automation) apparatus, for example, a word processor.
2. Description of the Prior Art
In conventional reflection type STN-LCDs provided with a phase difference plate as a color compensation plate, the product (d.multidot..DELTA.n) of the cell thickness and the refractive anisotropy is in the range of 0.81 to 0.83 .mu.m, and the retardation (Re) of the phase difference plate is 565 nm. The angle (.alpha.) formed by the liquid crystal molecular orientation axis of an upper substrate and an upper polarizer is about 50 deg., the angle (.beta.) formed by the liquid crystal molecular orientation axis of a lower substrate and a lower polarizer is about 50 deg., the angle (.theta.) formed by the liquid crystal molecular orientation axis of the upper substrate and the optical axis of the phase difference plate is about 105 deg., and the twisting angle (.phi.) of the liquid crystal molecule is about 240 deg.
The prior art STN-LCDs provided with a phase difference plate have the following problems:
(a) the background is colored in light green;
(b) the chromaticity changes largely as the temperature changes, and therefore a contrast which is stable against the temperature change cannot be obtained; and
(c) the chromaticity changes largely with the variations of the cell thickness and the retardation of the phase difference plate.